With the emergence of sheet metal CAD/CAM, control commands (NC commands) for numerical control (NC) machine tools can be output by just placing tools on CAD graphic processing lines, thereby freeing from tool address calculation as well as using calculation expert knowledge for executing NC commands. From the next stage of CAD graphics, outputting automatically executable NC data is currently possible using various methods.
Practical application technology for converting CAD data in unfolded sheet-metal representation drawn with CAD to executable NC data is made up of the following two-step process (see “SHEET METAL AUTOMATIC CAD/CAM SYSTEM CAMPATH FDM-II” Press Technology 1991, March Edition pp. 47-53 (THE NIKKAN KOGYO SHIMBUN, LTD., 1991)).
The flow of this process is described referencing FIG. 1. FIG. 1 shows a process flow for converting CAD data in unfolded sheet-metal representation drawn with CAD to executable NC data.
1) Process 1: Automatic Tool Assignment for Sheet Metal Expanded Graphics and Internal Generation of a non-executable NC Program
After converting unfolded sheet-metal graphic data generated with CAD (S102) to continuous lines in each shape unit, which represent a product outer line, window cut-out lines, and one-punch lines (as a formed louver that releases heat, the figure is completed through one punch using a forming tool instead of being a processed shape) are defined (S104). Subsequently, a pattern is specified by matching (S106) these continuous lines excluding the one-punch lines with a registered, processing shape pattern file having the same line segment data configuration.
A notched shape and window cut-out shape with variable product outer dimensions included in the sheet metal expanded graphics are processed with automatic tool assignment to each registered, processing shape pattern (S108). With automatic tool assignment, a tool is selected considering information of to-be-used material tensile strength and machine punching tonnage. Punch press sheet metal processing divides a processing shape into multiple processing regions, which are then processed in conformity with a combination of NC processing commands. Problems such as defective overlap processing around divided processing region boundaries, defective processing order, and processing direction as well as the defective shape of the tool to be used and defective processing commands become serious due to formation of material punched slug during processing. With automatic tool assignment, information of material lines, component outer processing lines, window cut-out lines, molding lines, and to-be-used tool shapes is referenced as information to consider these problems, so as to automatically determine the processing order and direction. Problems of unregistered processing shape portions (which should typically be assigned an outline processing tool and require manual correction) that are not assigned an automatic tool, and the defective results of automatic tool assignment are corrected by manual tool assignment (S110). Through these processing, the non-executable NC program (which includes a problem of processing machine damages as is) is internally generated (S112).
2) Process 2: Auto-Correction and Optimization of Non-Executable NC Program
The internally generated, non-executable NC program is automatically converted to an executable NC program, which allows actual processing (S114). This auto-correction and optimization process is incognizant of the processing constraints (such as exceeding the material adjustable range, tool path damaging the processing machine), and an auto-correction process for a manually generated NC program and/or an auto-generated NC program through auto-design and fabrication processes was implemented in the 1970's, wherein a similar process is applied to auto-correction and optimization.
In this manner, through Processes 1 and 2, the sheet metal expanded graphics generated using CAD is converted to an executable NC program.
As described above, after pattern determination in Process 1, a registered processing shape pattern is automatically divided into multiple processing shapes by referencing the tool assignment file for each pattern.
This automatic tool assigning function looks for a processing shape pattern corresponding to a size-variable shape, which has a line segment configuration registered in a sheet metal expanded graphics file (in which continuous line processing, product outer lines, window cut-out lines, material lines, and one-punch lines are defined) generated using CAD, that matches each general processing shape portion in sheet metal processing; thereby applying a corresponding already registered tool selection criterion, to-be-used processing commands, processing order and direction. Automatic tool assigning is implemented for an independent process for each pattern considering overlap processing of adjacent divided processing shapes, processing order, processing direction, or the like. Since unregistered processing shapes are subjected to an outline processing that may leave material slug, manual correction is needed. New processing shape patterns require additional processing; however, there are various types of shapes for every industry, and implementation of highly accurate automatic tool assignment is very difficult.
The above Processes 1 and 2 are basic technologies for automatic conversion of sheet metal CAD graphics to an NC program; however, the remaining greatest concern is solving the problem emanating from a lack of useful registered processing shapes, which are targets for automatic tool assignment.
With punch press machine sheet metal processing, finished products in a single processing industry (e.g., kitchen equipment, control panels, machine tool covers, building outer wall panels) may have the same shape; however, the expanded processing shape may differ for each user. As there are several expanded shapes of a die, various sheet metal part expanded shapes unique to a user develop since sheet metal products pursue specification limits for processing machines (processing size, sheet metal shape interference limitation for bending machines, and the like) and easy assembly fabrication. There are required patterns for the entire sheet metal industry, and thus demands for individual users cannot be met in the future.
There is a pattern backfilling method of controlling the number of registered processing shape patterns, and corresponding various patterns (see Japanese Patent Laid-open No. Hei 6-292930 ‘Tool assignment method for sheet metal processing graphics’). It is effective in controlling the number of registered patterns, but it does not resolve the problem for unregistered, newly processing shapes.
If there is precision in automatic conversion from a CAD file to an NC program, with current punch pressing, the environment with many restrictions managing and employing multiple NC programs, which are restricted to specified processing machines and mounted tool positions thereon, may be changed to an environment managing and employing only a CAD file. NC programs may also be output by selecting a target processing machine from the managed CAD file prior to processing.